1. Field of the Invention
This invention relates to an electromagnetic wave detector detecting an electromagnetic wave having a predetermined frequency band (infrared rays or an electromagnetic wave (a THz wave) having a THz frequency band) and, more particularly, to a bolometer-type light detector and an image pickup device providing therewith.
2. Description of Related Art
As one example of image pickup devices for picking up an infrared ray, a bolometer-type infrared image pickup device comprising one-dimensional or two-dimensional sensor array and a read-out circuit is known (see, Japanese Patent No. 3821040 (which will later be called Patent Literature 1)). The bolometer-type infrared image pickup device disclosed in Patent Literature 1 is configured to arrange a plurality of thermoelectric conversion elements in a two-dimensional matrix fashion and to detect and produce a received infrared ray signal every thermoelectric conversion element.
In addition, generally, a bolometer-type thermal infrared array sensor of the type described comprises a thermal separation structure composed of a diaphragm and beams (see, R. A. Wood, “Uncooled Infrared Image Arrays and Systems”, Semiconductors and Semimetals, Vol. 47, volume editors P. W. Kruse & D. D. Skartrud, Academic Press, 1997, p. 103 (which will later be called Non Patent Literature 1) and Japanese Patent No. 3597069 (which will later be called Patent Literature 2 and which corresponds to U.S. Pat. No. 6,495,829 B1)).
Patent Literature 2 discloses the thermal infrared array sensor in which an infrared full reflective film is formed on a substrate immediately below the diaphragm, a protection film of the diaphragm is made of a material which is transparent to the infrared ray, and an infrared absorption thin film with a vacuum impedance matching is formed on an upper surface of the diaphragm. A distance between the infrared absorption film and the infrared full reflective film is set to be a distance so as to absorb the infrared ray other than a predetermined wavelength band due to an interference to cancel to each other between the infrared absorption film and the infrared full reflective film.
Japanese Patent No. 5109169 (which will later be called Patent Literature 3 and which corresponds to U.S. Pat. No. 7,557,349 B2) discloses a bolometer-type THz-wave detector which has high performance and can be manufactured with high yield. The bolometer-type THz-wave detector disclosed in Patent Literature 3 detects a THz wave using an optical resonance structure used in of a bolometer-type infrared detector. Patent Literature 3 discloses, as a second embodiment, the bolometer-type THz-wave detector having structure where an absorbing film for absorbing the THz wave is added to a temperature detecting portion in order to efficiently absorb the THz wave having transmitted the temperature detecting portion. In addition, Patent Literature 3 also discloses, as a third embodiment, the bolometer-type THz-wave detector having structure where a canopy extending outward from the peripheral portion of the temperature detecting portion is formed on the temperature detecting portion.
Each of the thermistor bolometer thermal infrared array sensor disclosed in Patent Literature 2 and the bolometer-type THz-wave detector disclosed in Patent Literature 3 is provided with the optical resonance structure (an optical resonator) which causes the incident infrared ray or the THx wave to resonate in a traveling direction thereof. More specifically, a conventional optical resonance structure (a conventional optical resonator) uses an inter-gap resonance between the reflective film and the diaphragm (the temperature detecting portion). In the thermistor bolometer thermal infrared array sensor and the bolometer-type THz-wave detector each of which is provided with the conventional optical resonance structure (the conventional optical resonator) of such a structure, there is a limitation in performance of heat exchange. In other words, it is impossible to improve efficiency for converting electromagnetic energy into heat energy.